1. Technical Field
Several aspects the present invention relate to a silicon carbide substrate and a method for producing a silicon carbide substrate.
2. Related Art
Silicon carbide (SiC) is a wide band gap semiconductor having a band gap (2.36 to 3.23 eV) two or more times wider than that of Si, and has attracted attention as a material for a high-withstand voltage device.
However, since the crystallization temperature of SiC is high unlike Si, it is difficult to form a single crystal ingot by the same pulling method from a liquid phase as used for forming a Si substrate. Therefore, a method in which a single crystal ingot of SiC is formed by a sublimation method has been proposed. However, it is very difficult to form a substrate having a large diameter and few crystal defects by a sublimation method. On the other hand, among SiC crystals, cubic SiC (3C-SiC) can be formed at a relatively low temperature, and therefore, a method of performing epitaxial growth on a substrate has been proposed.
As one method for producing a SiC substrate using this epitaxial growth, a heteroepitaxial technique in which 3C-SiC is grown on a Si substrate in a gas phase has been studied. In the heteroepitaxial technique in which 3C-SiC is grown, a Si substrate is sometimes exposed to a high temperature of 1000° C. or higher. However, in such a heating process, Si atoms are sublimated from the Si substrate to cause a problem that the flatness of the Si substrate is deteriorated or the growth of 3C-SiC is inhibited.
In view of this, a method in which the sublimation of Si atoms is suppressed by carbonizing the surface of the Si substrate to form a SiC film (carbide film) has been studied. However, in the case where a defective part (pinhole) is present in the SiC film, Si atoms are sublimated from the Si substrate through this defective part. As a result, when 3C-SiC is grown on the SiC film by the heteroepitaxial technique, deterioration of the crystallinity of 3C-SiC is caused.
With respect to such a problem, NPL 1 (Journal of Crystal Growth 115 (1991) 612-616) describes that by increasing the pressure of a treatment gas (acetylene) to be used in the carbonization treatment, the defective part can be closed.
However, as a result of a detailed study made by the present inventors, it was found that the defective part once closed in the carbonization treatment reopens in the subsequent process. If the defective part opens in this manner, when 3C-SiC is grown on the SiC film, deterioration of the crystallinity of 3C-SiC is caused due to the effect of the defective part.